solar cooking and dehydrating

I want to build a solar oven and solar food dehydrator. Any suggestions on the best material for the 'glazing', the fiber glass piece that the sun light shines through? Where to find them, how much they cost, where can they be salvaged or scavenged? Will oven door glass be good enough?

I used to have a book on DIY solar oven designs.  As I remember it the key design features were reflectors placed at 120deg all around the glass to increase the solar energy being collected. The inside should be painted black to absorb the radiation. They were able to make solar ovens from a cardboard box, aluminum foil for reflectors, and oven grade plastic wrap! 

If you can salvage the window from a gas or electric oven, that would work great.

The cheapest glazing would be something like Rabid Chipmunk describes, although I think he means an oven-safe plastic bag, of the sort sold for baking Thanksgiving turkeys in.

A solar dehydrator runs at a lower temperature, and so an ordinary window would work. The best design I've seen uses a couple layers of black window screen at a very shallow angle as a solar collector/air intake bugscreen, and an insulated wall directly behind that. The air flows against the glazing, then is drawn through the sun-heated screen where it picks up most of its heat, then flows into the top of the (shaded) drying chamber. This whole thing is driven by a solar chimney, which draws from the bottom of the drying chamber.

Ordinary window glass? single pane, double pane? The model I am looking at has glass over a wood frame with black painted sheet metal on the otherside of the frame. below the metal would be the trays, and below them would corrugated metal roofing to allow airflow. I got the design from group in Minnesota.

Thanks for the specifics, "glazing" was very vague.

Has anyone mentioned that you can salvage the lens from a rear projection TV and use it as a giant magnifying glass?

That's for solar welding/smelting/blacksmithing, as much as solar cooking.

Hi Eric,

I may be the Minnesota source you referenced.  Glazing for the solar food dryer can be recycled glass - patio doors, old windows (no lead paint though) or shower doors work.  If using plastics you need one that can take the heat.  Greenhouse-grade plastics work well.  You do not need the twin wall insulated plastic.  If using polycarbonate, use the single layer version.  Acrylic window replacement glazing does NOT work.  It will crack in short order from the heat stress.

I don't know if you looked at our website, but there is a chart on the pros and cons of glazing materials on the food preservation page at http://www.geopathfinder.com/9473.html .

I like the idea of recycling old oven glass for a solar oven.  There is more thermal stress in an oven, and that would be a simple way to address that challenge.

Larisa

Larisa,
I think you are the source. I do like the model, the glazing has been hard to explain to salvage yards and window  places. When you say lead paint,  to you mean the frame or lead actually in the glass.

it depends where your focus is. I would say you really want two boxes, one to dehydrate and one to cook. In dehydrating you must have air movement but not so much heat. To cook you need heat and with most solar ovens, air movement takes away from that. I have been cooking my sons almond bread in an old crockpot base (the pot part broke from temp cycling) the lid happened to be clear. I put black painted foil in the bottom and covered a bakers sheet (half sheet) with foil as a reflector. I am at 49.5 deg north and still get 250F out of it even with the sun 25 to 30 off axis. (two hours before on axis). My cost was less than $1.

Solar cooking is great! It is so easy and cheap to try out and to play around with. Just wack up some card board boxes grab some foil and any old glass from the junk bin. Old coffee pots make a great "green house" for a black pained can to use as a small (muffin sized) oven or pot.... and can get hotter than the above with a corner reflector.

Len

Eric wrote:When you say lead paint,  to you mean the frame or lead actually in the glass.

Paint on the frame.

Lead in the glass would be OK, as far as I know, but panes of glass tend not to have lead in them: Leaded glass is mostly to look at, not to look through.

Joel Hollingsworth wrote:
That's for solar welding/smelting/blacksmithing, as much as solar cooking.

Solar.........                          .....welding?!



Solar...  ..blacksmithin...?!